The Vajont landslide, which occurred on October 9, 1963is perhaps the most tragic example of a natural disaster triggered by human activity.
It was the consequence of still immature technical knowledge, errors, considerations and incorrect technical interpretations on the part of the cream of engineers, geologists and geophysicists of the time.
- 1The construction of the Vajont dam
- 2Two signals before the big landslide
- 3Who were Leopold Muller and Edoardo Semenza
- 4The real cause of the Vajont landslide?
- 5What happened on the day of the Vajont disaster?
- 6Three points for reflection on the Vajont landslide
The construction of the Vajont dam
The Vajont dam was designed by the engineer Carlo Semenza and was built between 1956 and 1960. This mega structure was commissioned by the Adriatic Electricity Company, known as SADE. Why was there a need to build a dam?
The project in itself was crazy from an engineering point of view, a true marvel for the economy of the time, because hydroelectric power was one of the main sources of energy in Italy (as it is today) and the Grande Vajont system it would have contributed to feeding practically the entire Triveneto.
But the engineers did the math without the innkeeper: the valley was unsuitable for the construction of an artificial basin, precisely because of theslope instability of the invasion. But when work began in 1957, no one had taken it seriously into consideration.
Two signals before the big landslide
Before the great landslide, which occurred on 9 October 1963, there were already some disturbing signs: in 19593 million m3 of rock collapsed in the Pontesei basin, one of the basins of the Great Vajont system; there was no damage but the alarm bells went off among the workers and others.
The alarm bells became even louder with the November 4, 1960 when there was another landslidesmaller, but it occurred right in the basin of the Vajont dam, and caused a two-meter wave. There was no damage or victims because the water did not exceed the dam but from that moment Carlo Semenza himself began to be seriously worried.
Many experts were involved, geologists, geophysicists, engineers, who made many errors of evaluation and interpretation, not understanding that “everything” could come down there.
Who were Leopold Muller and Edoardo Semenza
At this point two of the main characters of the story enter the scene: the first was the geologist Leopold Mullerconsidered one of the pioneers of geomechanics; I would venture to say that he was closer to the profile of a geotechnical engineer than a pure naturalist geologist; in fact he was not an expert on landslides. To be honest, at that time there were no great landslide experts because landslides began to be studied with a new methodology and a high level of detail precisely after the Vajont disaster. I know it’s sad but it’s the reality of the facts.
And I’ll tell you more, not only did landslides begin to be studied at a certain level, but an entire scientific branch, geotechnics, was truly born after the Vajont disaster.
1963 was the beginning of a new era for geotechnical sciences, the study of soils, slopes, landslides and rock mechanics.
Beyond Muller there was Edoardo Semenzason of Carlo Semenza, the designer of the dam.
Muller was a giant, Edoardo was far less successful: a boy in his thirties, recently graduated.
Since a large and visible fracture formed on the mountain, both of them, like all the other experts involved, agreed that there was a landslide but had a different interpretation of the type of landslide and the type of danger.
Muller believed that the landslide was a geologically recent landslide, and that it was characterized by slow movement, like a glacier. Instead, according to the young Edoardo, who went to analyze every square meter of the mountain with his eyes (with a purely empirical and scientific approach), the landslide was a paleolandslide, that is, old, which had existed for who knows how long. According to him, it could have detached suddenly, sliding with a relatively sudden movement, and ended up in the basin causing monstrous waves and unimaginable damage.
Edoardo seemed to be the “catastrophist” of the situation and in fact no one gave him much consideration: he was too young and too inexperienced for his theory to be taken into serious consideration.
The real cause of the Vajont landslide
The landslide was moving about 3 cm per day, it seemed to be slow as Muller said. And Muller also thought of one thing: that the speed of the landslide depended on how much water was present in the artificial lake of the dam. The more water there was, the faster the landslide moved.
The reason was linked to the presence of a clayey level, below the rocks emerging on the surface, which by absorbing water, acted as a lubricant, and favored sliding.
“Wow” – they all thought – “so if the water level is reduced, the landslide will slide more slowly?!” It seemed to be like this… in reality it really was: by lowering the water level, in fact, it went from 3 cm per day to 1 mm per day.Well, this was the biggest mistake: the belief crept in that they had the solution to the problem in their hands: that is, being able to use water as a kind of brake and accelerator, thus controlling the sliding of the landslide. They wanted to make the landslide slide specifically so as to avoid a single sudden collapse that could cause who knows what damage.
The technique of varying the water level was continued for two years.
In June 1963 the flood level of the basin reached i 700 m above sea level, reporting the landslide to a slide of 5 mm per day.
In that period there was a handover in the management of the plant from the private to the public, and precisely in that period (and here there was another enormous mistake on the part of many people and workers) the level of the basin was lowered with delay: the water came up to approx 710 m above sea level and the landslide reached a speed of 2 cm per day. Only on 26 September 1963 the basin was brought back to the safe level, but it was already too late.
What happened on the day of the Vajont landslide
On October 9, 1963, at 10.39pmit was now dark, what Edoardo Semenza had predicted happened: 270 million m3 of rock, we are talking about an entire face of a mountain, broke away from Mount Toc (a measurement that no one had managed to predict before the event); the movement of the landslide was rapid; imagine cutting a slice of mountain and letting lubricating oil penetrate the fracture; the landslide slid down in one piece within 20 or 30 seconds, at a speed of between 70 and 90 km per hour.
When it arrived in the basin, a monstrous wave was generated, which went up the slope of the mountain in front, almost touching Casso; part of the municipality of Erto, also on the opposite bank, was destroyed; the precise dynamics of the water movements were not filmed by any camera of the time so there are no real images but the wave was so large that a good part of the water set in motion literally went over the dam, ending up down in the valley with such violence as to destroy the town of Longarone.
Unfortunately the victims were 1920.
Three points for reflection on the Vajont landslide
The Vajont disaster is a tragic event which, today, sixty years later, should make us reflect on some points.
- We are ants towards natural phenomena; we must remember that you don’t joke with nature, otherwise you risk getting very hurt.
- The economic and political interests too often they take over the environment; today perhaps compared to 1963, something has improved, but we are still very far from where we should be. In this context, scientific and cultural dissemination play and will play a very important role in spreading further responsibility towards the environments in which we live.
- Too often we understand things only after there are tragedies, disasters or victims. After the Vajont disaster, great interest in geology and landslide events exploded.
In this regard, I would like to take up a passage from a 2013 article by my colleague Aldo Piombino:
Applied Geology was born with this tragedy. Yes, there were already courses in Geology Applied to Engineering, but most of those who studied the subject were engineers, not geologists. Leopold Muller was also an engineer, albeit a “geological engineer”, as there are construction workers, mechanics, electronics etc etc. It was from that moment that in the world of Earth Sciences someone also began to deal with landslides, aquifers , tests on materials, deformations and so on in addition to the many who until then had dealt with the history of the Earth, volcanoes and how mountain chains arose.
The PODCAST by Andrea Moccia on the reconstruction of what happened